Dialysis is a blood purification procedure used in the case of renal failure as a replacement method. Apart from renal transplantation, dialysis is the most important renal replacement therapy in the case of chronic renal failure and one of the possible alternative treatments in the case of acute renal failure. It is the aim of dialysis to keep the concentration of substances that are usually eliminated with the urine or are pathogenic, as the case may be, in the blood and/or in the body of the patient below a toxic limit.
Blood purifying therapy procedures are based on the physical basic principles of diffusion, osmosis and convection and partly also adsorption. The different procedures of dialysis are usually based on exchange of substance via specific semipermeable membranes hereinafter referred to as dialyser membranes. Inter alia, dialysis causes the purification of the blood, the removal of water from the blood circulation and the addition of electrolytes to the blood. In dialysis on one side of the dialyser membrane there is provided blood or blood plasma and on the other side of the membrane there is a dialysis solution or a dialysis fluid, respectively. Depending on the nature of the membrane, different substances diffuse through the membrane from the blood into the dialysis fluid and in this way are removed from the blood circulation. At the same time, other substances such as electrolytes can also diffuse from the dialysis fluid into the blood. One of the crucial parameters is the nature of the membrane and especially the pore size thereof substantially determining which substances are removed from the blood during dialysis. The use of such semipermeable membranes therefore is also referred to as selective diffusion. While the membrane substantially determines the type and the size of the basically exchangeable substances, the diffusion rate and thus the actual exchange is substantially determined by the differences in concentration of the respective substances on the different sides of the membrane. The substances to be removed are roughly classified into low-molecular, medium-molecular and high-molecular substances. Moreover, the water balance of the patient can be controlled by osmosis or a pressure difference artificially produced between the different sides of the dialyser membrane by liquid being removed from the blood to be purified. In addition, specific additives in the dialysis fluid are adapted to influence and regulate the acid-base state and the electrolyte composition of the blood.
The dialyser membranes used are, on the one hand, artificial or technical membranes, but on the other hand also endogenous physiological membranes. Hence in dialysis a distinction is made between extracorporeal procedures using artificial membranes outside the body and intracorporeal procedures performed inside the body and making use of endogenous membranes.
An example of an intracorporeal dialysis procedure is constituted by the peritoneal dialysis in which the peritoneum is used as membrane for blood purification. In this case the dialysis fluid is directly introduced through a catheter port into the peritoneal cavity of the patient and is exchanged as dialysate after completed equilibration of the substance concentrations. Typically, in this way three to six exchanges of the dialysis fluid, distributed over one day, having a volume of about 2.5 to 4 liters each are performed. In order to avoid negative health consequences for the patient, the dialysis fluid has to be brought to body temperature each time before being introduced into the peritoneal cavity.
An example of an extracorporeal dialysis procedure is the hemodialysis applied most all over the world. This procedure pursues the principle of concentration balance of small-molecular substances of two fluids which are separated outside the body in a dialyser by an artificial semipermeable dialyser membrane. Being separated by the dialyser membrane, on the one side the blood including nephrotoxins, electrolytes such as potassium and phosphate as well as substances usually eliminated with the urine is provided. On the other side of the dialyser membrane a low-germ processed solution is provided as dialysis fluid which contains no waste products and includes a share of electrolytes oriented at the respective needs of the patient. The semipermeable dialyser membrane between blood and dialysis solution or dialysis fluid, resp., has pores allowing small molecules such as water, electrolytes and substances usually eliminated with the urine (e.g. urea, uric acid) to pass but withholding large molecules such as proteins and blood cells.
In the procedure of hemodialysis three to four treatments for about 4 h per week are typical. For each treatment a considerable amount of dialysis fluid is required which permanently bypasses the membrane on the side of the dialyser membrane facing away from the blood. Frequently, the dialysis fluid is guided to the blood in a counter-current. The dialysis fluid is discharged as dialysate after single use when enriched with substances usually eliminated with the urine. In general, for reasons of unambiguous assignment, the fluid used for dialysis is referred to as dialysis fluid prior to being enriched with substances usually eliminated with the urine, whereas the fluid enriched with the substances usually eliminated with the urine is referred to as dialysate. The quantity of dialysis fluid consumed can amount to 100 l and more for each application. Solely the large quantity of dialysis fluid to be produced and consumed renders a dialysis treatment extremely costly. In addition to the high consumption of resources, the energy consumed to process the dialysis fluid considerably increases the costs.
Apart from the quantity of the fluid supplied and/or withdrawn from the blood, also the temperature of the blood has to be exactly controlled so as to prevent serious damage to the patient. The blood supplied to the patient again after its purification must have a temperature dependent on the body temperature of the patient so as to avoid such damage to the health. This is obtained by heating the dialysis fluid and thus also the dialyser membrane and the components surrounding said membrane to body temperature so as to prevent the blood from cooling in the extracorporeal circulation.
Before the dialysis fluid is passed by the blood of the patient by means of a dialysis unit in a dialyser including the filter membrane, it is thus heated from the input temperature (typically 10° C.) to a higher temperature approximately at the level of the blood temperature (typically 36° C.). When the dialysate has flown through the dialysis filter, it is used up and is discharged in the outlet. Said tempering of the large quantity of dialysis fluid consumes a considerable amount of additional energy.
In the extracorporeal methods such as hemodialysis (HD) moreover after each dialysis treatment the apparatus used, i.e. the dialyser, should be sterilized in order to prevent cross-infection between individual patients. For this purpose, the so called hot disinfection is frequently applied. In this case a water/disinfectant mixture is heated in the dialysate circulation of the dialyser to >85° C. and is circulated for a particular time, typically about 15 minutes. After expiry of this period of time, the disinfectant should be rinsed out as quickly as possible and the machine or the dialyser, as the case may be, as quickly as possible should be cooled to approx. 35° again so as to enable the next therapy.
As further extracorporeal dialysis procedures hemofiltration or hemodiafiltration are mentioned by way of example only which partly consume even higher amounts of resources and energy and therefore incur similar or higher costs when being applied.
Due to the high consumption of resources and the high energy consumption for a dialysis treatment, there is a considerable need to render dialysis units and procedures for operating dialysis units more efficient.